A vehicle data processing apparatus such as a navigation system, which is mounted in a vehicle and performs predetermined data processing, operates upon receiving a power supply from a vehicle battery or another in-vehicle device when a vehicle drive switch (specifically, accessory switch, ignition switch, etc.) is in an on state.
Therefore, in the vehicle data processing apparatus of that type, when the vehicle drive switch becomes in an off state, data (for example, position data of the vehicle in the navigation system) required for data processing after starting next time is saved in a backup memory circuit (for example, refer to Patent Literature 1 and Patent Literature 2).
Incidentally, in the conventional art, it is assumed that a backup power is supplied to the vehicle data processing apparatus from an internal battery or the vehicle battery for at least a period of time required for backing up data since the vehicle drive switch turns off.
In other words, even if the accessory switch or the ignition switch turns off to cut off a main power supply, data can be written into a memory circuit.
For that reason, in the vehicle data processing apparatus in which a power supply route from the in-vehicle device is of one system, and no backup internal battery is provided, the above conventional art cannot be applied, and data cannot be backed up at the time of cutting off the power supply.
On the other hand, as a method for solving the above problems, it is conceivable that when the vehicle drive switch is in the on state, and the power is supplied from the in-vehicle device to the vehicle data processing apparatus, data is periodically written into the memory circuit (in this example, nonvolatile memory that can hold data without receiving the power supply).
However, in the case where data is periodically written as described above, when the period is long, data immediately before the vehicle data processing apparatus stops the operation cannot be saved in the nonvolatile memory.
When the period in which data is written into the nonvolatile memory is shortened, data immediately before the vehicle data processing apparatus stops the operation can be saved. However, in that case, a frequency at which data is written into the nonvolatile memory increases.
As a result, the above case causes such a problem that the number of writing data into the nonvolatile memory reaches the number of times for compensation in a short period of time, the life of the nonvolatile memory is shortened, and the exchange of the nonvolatile memory is required.